1. Field of the Invention
The embodiments of the invention relate to a display device, and more particularly, to an apparatus and method for driving a liquid crystal display (LCD) device. Although embodiments of the invention are suitable for a wide scope of applications, it is particularly suitable for partially emphasizing brightness of an image.
2. Discussion of the Related Art
Generally, an LCD device displays an image on an LCD panel by controlling transmittance of light provided from a backlight unit. The LCD panel includes a plurality of liquid crystal cells arranged in a matrix configuration and a plurality of control switches to switch a video signal supplied to the liquid crystal cells. The backlight unit can have a fluorescent lamp as a light source. The trend in backlighting technology is toward smaller, thinner, and lighter backlight units. Based on this trend, light emitting diodes (LEDs) have been proposed as substitute for fluorescent lamps since LEDs have the advantage of low power consumption, light weight, and high brightness.
FIG. 1 is a schematic of an apparatus for driving an LCD device using an LED backlight unit of the related art. As shown in FIG. 1, the related art driving apparatus includes an LCD panel 2 having liquid crystal cells respectively formed in regions defined by n gate lines (GL1 to GLn) and m data lines (DL1 to DLm); a data driver 4 that supplies an analog video signal to the data lines (DL1 to DLm); a gate driver 6 that supplies a scan signal to the gate lines (GL1 to GLn); a timing controller 8 that controls the data driver 4 and the gate driver 6, and generates a dimming signal (DS) using input data (RGB); and an LED backlight unit 10 that generates light from a plurality of LEDs corresponding to the dimming signal (DS) and supplies the light to the LCD panel 2. A thin film transistor array substrate and a color filter array substrate are bonded together with a spacer between the two substrates to maintain a cell gap as well as liquid crystal in the space between the two substrates to form the LCD panel 2.
Liquid crystal cell are defined by the gate lines (GL1 to GLn) and the data lines (DL1 to DLm) on the thin film transistor array substrate. A thin film transistor (TFT) is formed in each of the liquid crystal cells. Each TFT supplies an analog video signal provided from the data line (DL1 to DLm) to a liquid crystal cell in response to the scan signal provided from the gate line (GL1 to GLn). Each liquid crystal cell can be equivalently expressed as a liquid crystal capacitor (Clc) because it is provided with liquid crystal between a common electrode and a pixel electrode connected with the TFT. Each liquid crystal cell also includes a storage capacitor (Cst) that maintains the analog video signal charged on the liquid crystal capacitor (Clc) until the next analog video signal is charged thereon.
The timing controller 8 arranges externally supplied source data (RGB) to be appropriate for the driving of the LCD panel 2, and provides the arranged source data to the data driver 4. Also, the timing controller 8 generates a data control signal (DCS) and a gate control signal (GCS) by using a dot clock (DCLK), a data enable signal (DE), and horizontally and vertically synchronized signals (Hsync and Vsync) externally inputted thereto, and provides the generated control signals to the data driver 4 and the gate driver 6, to thereby control driving timing of the data driver 4 and the gate driver 6. The timing controller 8 also generates the dimming signal (DS) to control the LED backlight unit 10 by using the input data (RGB).
FIG. 2 is a graph illustrating a dimming curve to control an LED backlight unit of the related art. To generate the dimming signal (DS), the timing controller 8 detects the average brightness of the input data (RGB). As shown in FIG. 2, the timing controller 8 then extracts a dimming value corresponding to the detected average brightness (Avg) from a dimming curve (A) set based on the brightness characteristics of the LED backlight unit 10, and generates the dimming signal (DS) based on the dimming value. In FIG. 2, the X axis shows the average brightness (Avg) of the input data (RGB), and the Y axis shows the dimming value corresponding to the dimming curve (A). The dimming curve (A) has an increased dimming value as the gray scale becomes brighter corresponding to the brightness properties of LED backlight unit.
Referring to FIG. 1, the gate driver 6 includes a shift register which sequentially generates the scan signal, that is, a gate high signal in response to the gate control signal (GCS) supplied from the timing controller 8. The gate driver 6 sequentially supplies the gate high signal to the gate lines (GL) of the LCD panel 2 such that the TFT connected with the gate line (GL) is turned-on.
The data driver 4 converts the data signal (Data) provided from the timing controller 8 to the analog video signal in accordance with the data control signal (DCS) supplied from the timing controller 8, and supplies the analog video signal for one horizontal line to the data lines (DL) in one horizontal period for supplying the scan signal to the gate line (GL). That is, the data driver 4 selects a gamma voltage having a predetermined level based on the gray scale value of the data signal (Data), and supplies the selected gamma voltage to the data lines (DL1 to DLm). Then, the data driver 4 inverts the polarity of the analog video signal supplied to the data lined (DL) in response to a polarity control signal (POL).
The LED backlight unit 10 includes an LED array 12 having a plurality of LEDs and an LED controller 14 that drives the LEDs in accordance with the dimming signal (DS) supplied from the timing controller 8. The LED controller 14 generates a pulse-width modulation signal (Vpwm) corresponding to the dimming signal (DS), and provides the generated pulse-width modulation signal (Vpwm) to the LED array 12. The LED array 12 is positioned opposite to the rear surface of the LCD panel 2. The LED array 12 can include a plurality of red, green and blue LEDs arranged repeatedly. The LEDs generate the light in accordance with the pulse-width modulation signal (Vpwm) supplied from the LED controller 14, and then the generated light is applied to the LCD panel 2.
In the above apparatus for driving the LCD device using the LED backlight unit of the related art, the scan signal is supplied to each gate line (GL), and the input data (RGB) is converted into the analog video signal and is then supplied to each data line (DL) in synchronization with the scan signals, to thereby drive the liquid crystal cells. Simultaneously, the plurality of LEDs are driven by the pulse-width modulation signal (Vpwm) corresponding to the dimming signal (DS) in accordance with the average brightness of input data (RGB) from one predetermined dimming curve (A). Accordingly, the apparatus for driving the LCD device using the LED backlight unit of the related art controls the transmittance of light supplied from the LED backlight unit 10 through the liquid crystal cell driven by the analog video signal, to thereby display the image on the LCD panel 2 corresponding to the input data. However, the apparatus for driving the LCD device using the LED backlight unit of the related art has the following disadvantages.
In the apparatus for driving the LCD device using the LED backlight unit of the related art, the dimming signal (DS) is generated based on one predetermined dimming curve (A) from the average brightness of input data (RGB). Accordingly, it is impossible to partially emphasize the brightness of the image displayed on the LCD panel 2 by using the LED backlight unit. Also, the brightness of the LED backlight unit is determined within one predetermined dimming curve (A), which limits variation of brightness in accordance with the input data (RGB), which can cause an unnecessary increase in power consumption.